1. Field of the Invention
This invention has to do with the formulation of compounds to be used in the polishing of surfaces such as aluminum surfaces used for magnetic recording.
2. Prior Art
Principles in the art of polishing are well understood and have been practiced for many years. A polishing medium is formulated which consists of hard abrasive particles. The particles should be harder than the surface to be polished. The particles are supported in a supporting medium which is softer than the medium to be polished. The polishing medium is rubbed across the surface to be polished while simultaneously a liquid is applied which lubricates the surface to prevent ingredients of the polishing medium from sticking to the surface and to wash away wear debris.
Many kinds of abrasive particles have been used in this application--alumina, silicon carbide, silica, ceria, diamond,--to name a few.
Many kinds of supporting media have been used--cloth, tar, tin, glues, resins, including foams.
Many kinds of liquids have been used as lubricants,--kerosene, water soluble oils, etc.
Many tecniques are used for charging the abrasive into the supporting medium. For example, for polishing ceramics, diamond powder is the abrasive of choice; tin is the supporting medium. Tin is electroplated onto a steel backup plate and the diamond is rubbed into the tin plate so that only a part of the diamond protrudes to polish the ceramic surface.
Another technique, used for the polishing of semiconductor wafers, is to supply the abrasive as a liquid slurry. Aquaeous based liquids are available commercially which cantain colloidal sized silica particle (10-50 Angstroms in size). These liquids are available from the Dupont corporation, Dover, Del. under the trade name, Ludox. The liquid is applied to polishing pads, such as felt and rubbed onto the surface to be polished. Normally, silica particles in this size range are unstable and coalesce to form larger particles. In order to stabilize the particles against growth, polishing solutions such as Ludox contain a base--e.g. sodium, ammonia, etc. Thus, the polishing action is the result of very fine particle size and the reactivity of the solution.
The chemical reactivity of the solution can be a problem with some materials. Furthermore, the requirement to add solution continuously introduces an additional parameter into the control of the polishing and is expensive.
It is an objective of this invention to provide a polishing medium in which the abrasive particle sizes are of colloidal dimensions, do not react with the surface being polished, and are applied uniformly in a manner which does not require careful control as with the liquid containing abrasive.
Another technique is to incorporate the abrasive into the support matrix. This has been done using glues and various other resins as the supporting matrix. The problem with this technique is to obtain a very uniform dispersion of the particles and preventing the particles from clumping. Powders of fine particle size are expensive because of the necessity to grade them. For this reason it is not practical to use powders in the above manner where the particle sizes are less than about five microinches. Furthermore, there is no chemical bonding of the particles to the matrix. Consequently, the polishing medium is weakened by incorporation of the powders so that the polishing medium tends to wear. This mitigates against providing a flat polished surface particularly at the edges.
It is a further objective of this invention to provide a polishing medium which contains very fine abrasive particles, below a microinch in size and preferably in the size range from 10 to 50 nanometers which are very evenly distributed throughout the support matrix, are chemically bonded to the support matrix to provide strength and do not contain large particles or agglomeration of particles that would otherwise scratch or roughen the surface to be polished.
These and other advantages of this invention will be apparent to one skilled in the art of polishing after further examination of the drawings and description.